This invention relates to a misfire detecting device for detecting the occurrence of misfire in an internal combustion engine.
There are available a variety of misfire detecting devices for internal combustion engines. Japanese Patent Application (OPI) No. 19532/1983 (the term "OPI" as used herein means an "unexamined published application") has disclosed a misfire detecting device which is based on deflections in revolution of an engine. The device detects the difference between the speed of revolution in the first half of an expansion stroke of the engine and that in the second half, to determine whether or not a misfire has occurred.
Another example of the conventional misfire detecting device is designed as follows: A revolution period deviation is detected every ignition period, and it is divided by a predetermined average value of revolution period, to obtain a revolution deflection coefficient. The coefficient thus obtained is utilized to determine the presence or absence of a misfire.
As was described above, the conventional misfire detecting device operates on the deflections in revolution of the engine; that is, it detects the occurrence of a misfire on the fact that, when a misfire occurs in an engine, the period of revolution of the cylinder where the misfire has occurred is increased. However, effects of its revolution detecting segment are not taken into account. That is, the device suffers from the difficulty that the mechanical dimensional error of the revolution detecting segment is superposed on a revolution signal, as a result of which an erroneous decision is made on the occurrence of a misfire.